Spring suspension for tandem axle trucks



6 Sheets-Sheet l A. F. HICKMAN SPRING SUSPENSION FOR TANDEM AXLE TRUCKS i i H g U\% QZ-Eorvqys.

Dec. 22, 1953 Filed Dec. 7, 1951 Dec. 22, 1953 A. F. HICKMAN SPRING SUSPENSION FOR TANDEM AXLE TRUCKS 6 Sheets-Sheet 2 Filed Dec. 7, 1951 Dec. 22, 1953 A. F. HICKMAN SPRING SUSPENSION FOR TANDEM AXLE TRUCKS 6 Sheets-Sheet 3 Filed Dec. 7, 1951 Dec. 22, 1953 A. F. HICKMAN SPRING SUSPENSION FOR TANDEM AXLE TRUCKS 6 Sheets-Sheet 4 Filed Dec. '7, 1951 wm MMN mw QA D 22, 1953 A. F. HICKMAN SPRING SUSPENSION FOR TANDEM} AXLE TRUCKS 6 Sheets-Sheet 5 Filed Dec. 7, 1951 INVENTOR.

A. F. HICKM'AN SPRING SUSPENSION FOR TANDEM AXLE TRUCKS Filed Dec. 7, 1951 Dec. 22, 1953 Md-W &

Patented Dec. 22, 1953 UNITED STATES PATENT OFFICIE SPRING SUSPENSION FOR TANDEM AXLE TRUCKS This invention relates to a spring suspension for tandem axle trucks in which the resiliency is provided by rubber springs of the shear rubber, rectilinear movement type.

One of the important objects of the present invention is to provide a shear rubber, rectilinear movement type of spring suspension for tandem axle vehicles which will permit the large amount of vertical axle movement necessary with highway vehicles to provide a vertical ride as soft as load heights will allow and at a low frequency, in the order of 105 to 110 cycles per minute at the rear end of conventional trucks when empty, and at a frequency close to 100 cycles per minute under full loads.

Another important object of the invention is to provide such a suspension which is substantially free from friction out is automatically controlled by an increasing resistance to motion in proportion to the amplitude of vertical frame and axle movement relative to each other.

Another object is to provide such a suspension in which lateral and vertical movement of the axles with reference to the vehicle frame are permitted and resiliently resisted, the lateral and vertical resilience being sufficient, both when the vehicle is loaded and unloaded, to absorb lateral thrust of the axle, particularly resulting from one wheel moving up and down, thereby to provide increased safety, tire and gasoline mileage, and stability, and without imposing undue end thrusts on the pivotal connections which connect the axles to the frame.

Another object is to provide such a suspension which includes compensating means connecting the companion ends of the tandem axles and through which the excess load on either axle is transmitted to the other axle and in which this compensating or load transfer means is in the form of a simple transmission arranged so that the total load on both axle ends is transmitted to a common spring support for each pair of axle ends, this spring support being of the rectilinear movement, shear rubber type.

Another object is to provide such a compensating or load transfer means in which the transfer of load from the tandem axles to the front axle of the vehicle, under braking reaction, is identical with the similar transfer of load in a two axle vehicle of the same wheel base, weight and load.

Another object is to provide such a suspension in which the distribution of the load to the body is at a plurality of well spaced points to reduce frame stresses.

2 Another object is to provide such a suspension in which side sway can be reduced to any desired amount.

Another object is to provide such a suspension in which periodic vibration of the suspension is dampened out and in which wheel tramp is avoided.

Another object is to provide such a suspension which is very light in weight, particularly in unsprung weight, as compared with conventional suspensions.

Another object is to provide such a suspension consisting of compact units which can be arranged without interference with the movement of the axles with respect to the frame and in which the parts are arranged inside the wheels and close to the wheels to provide high and wide pivot positions and increased stability.

Another object is to provide such a suspension which is simple in construction and is composed of low cost parts which can be readily taken down and repaired and which will stand up under conditions of severe and constant use with very little servicing.

Another object is to provide such a suspension which renders radius rods or auxiliary devices for the control of side sway, such as torsion bar stabilizers, unnecessary, and at the same time adequately resists all brake and drive torque reactions.

Another object is to provide such a suspension in which any desired frequency or degree of spring deflection can be obtained and which can be designed to have a long and variable spring resistance range in both vertical and lateral axle movements.

Another object is to provide such a suspension which will fit trucks having wide frames and large tires.

Another object is to provide such a tandem axle suspension in which the tandem axles are self-steering so that when rounding a curve the tandem axles are caused to assume such an angle relative to each other as will enable a pure rolling action to be obtained.

Another object is to provide a vehicle sus-- pension which can be easily serviced and in particular in which the shackles of the suspension, which require the most frequent servicing, can

be readily removed on jacking up the vehicle 7 body and replaced with new or factory rebuilt shackles, thereby to avoid a difficult field operation and also to avoid withholding the truck from service for any great length of time.

Another object is to provide such a suspension employing rubber blocks or bodies in rectilinear shear and in which the bond stress of the rubber is kept within safe working limits.

Other objects and advantages of the invention will be apparent from the following description and drawings in which:

Fig. 1 is a side elevation of the rear end of a tandem axle vehicle having a suspension embodying the present invention, the axles and drive shafts being shown in a section taken along line of Fig. 2.

Fig. 2 is a fragmentary top plan view of the suspension shown in Fig. 1.

Fig. 3 is a fragmentary rear thereof.

Figs. 4, 5 and 6 are vertical transverse sections taken on the correspondingly numbered lines of Fig. 2.

Fig. 7 is a fragmentary vertical section take'n on line Fig. 3.

Fig. 8 is a fragmentary horizontal section taken generally on line 8-3,' Fig; 3. v

Fig. 9 is an enlarged fragmentary vertical section taken on'line 99, Fig. 8.

Figs. 10, 11 and 12 are fragmentary sections similar to Fig. 9 and showing the position of the parts under different load conditions, Fig. showing the position of the parts when the vehicle is carrying a normal load; Fig. ll showing elevational view the position of the parts when a severe bump in the road is encountered by the vehicle when fully loaded; and Fig. 12 showing the position of the parts when the vehicle is unloaded.

Fig. 13 is an enlarged vehicle transverse section taken generally on line |3--|3, 1, parts being broken away, and this view showing by dotted lines successive positions of the parts when the vehicle is loaded and when the suspension is worked to its full capacity.

Fig. 14 is a vertical section taken generally on line i |4, Fig. '13.

Fig. 15 is a horizontal section taken generally on line 15-45, Fig. 14-.

Fig. 16 is a perspective view of one of the T- shaped backing plates used in connection with the suspension.-

In the form of the invention illustrated in the drawings, the main frame E5 of the vehicle can be of any suitable construction and is shown as comprising a pair of longitudinal side frame bars in the form of inwardly facing channels 20 which are shown as straight and parallel and as pro vided with reinforcing'channel liners extending substantially the full length thereof. These channels 26 together with their liners 2! are shown as connected at their rear ends by a cross bar 22 of channel configuration and reinforced by horizontal triangular gusset plates 23'. advance of the tandem axles the longitudinal side frame bars 20, 2| are connected by a cross bar 25 and reinforced by horizontal triangular gusset plates 26. of rectangular tubular form in cross section.

The frame additionally includes a. structure, indicated generally at 28. connecting the side frame bars 20, 2| and disposed midway between the tandem axles. This connecting structure 'is' preferably constructed as follows:

The numeral 29 represents a main cross bar.

Each end of this U-shaped cross bar 29 is sup,

ported on the horizontal leg of an L-shaped supporting bracket 3 the vertical leg of which, as

The cross bar 25 is preferably 1 best shown in Fig. 13, is disposed against the face of the liner 2| for the corresponding channel 2|! and secured to the liner 2| by welding or otherwise.

Each end of this U-shaped cross bar 29 is ad ditionally connected to each side frame bar 20, 2| by upper and lower gussets designated at 32 and 33, respectively. The upper gusset 32 is L- shaped in cross section and'has an upper horizontal part 34 which overlies and is suitably secured to the corresponding end of the U-shaped cross bar 29 and also has a vertical part 35 which ing on the lower flange ofthe liner channel 2| and secured thereto in anysuitable manner.

The front and rear ends of each gusset 33 are connected to the bracket 130 of a bearing indicated generally at 4| and which bracket comprises a metal cylinder 42 arranged with its axis lengthwise of the frame and a pair of spaced vertical webs 53 connecting this cylinder with an L-shaped attaching-bracketed the horizontal leg 65 of'which is attached by" bolts 45 to the underside of the side frame bar 22, 2| and the vertical leg as of which'is attached by a bolt 49- to the vertical part 38 of the "Z-shaped gusset 33. A similar bearing bracket 40 is arranged under each end of the cross bar 25 and which is similarly connected to the frame by a bracket 50 which, as with the gusset 33 and as best shownin Fig. 4, is of general Z-sha'pe in cross section having an upper horizontal part 5| suitably secured to the underside of the cross bar 25, a ver-' tical part 52 arranged parallel with but spaced from the side frame bar 20, 2I'and a horizontal part 53 resting on the lower fiange. of the liner channel 2| and secured thereto in any suitable: A similar bearing bracket as is are.

manner. 7 ranged adjacent each end of'the rear cross bar 22 and is connected to' the frame, as best shown in Fig. 6, by a generally U-shaped bracket 5A,

the horizontal legs of which are suitably secured to the underside of the' corresponding gusset. 22

and to the lower flange of the liner 2|. The vertical part 55 of each bracket 54 is disposed in wardly of and in spaced relation to the COIl'G-I' spending side frame bar 20, 2|.

This frame is shown as supported by a pair oftandem axles and 5| which are supported by wheels 62, these'wheels being rotatably secured to the axles. be drive wheels, both axles being shown for this purpose as housing drive shafts 63 connected by the usual differential gears not shown) and se cured to the wheels 62 in the usual and wellknown manner.

The construction of the tandem axle springsuspension at the left hand'side of the truck is the same as the tandem axle spring suspension at the right hand side of the truck'and hence a:

description of the spring suspension at one side of the truck willbe deemed to applyto both sides,

the same reference numerals b'eing'used.

A feature of the invention resides in the use of four rubber shear springs, indicated generally at 65, in the spring suspension to provide the resilient support for the frame I9 on the tandem axles 60, 6|.

One or both groups of wheels can While this number is not critical,"

eachof these rubb'er 'shear springs 55 1s shown as mounted on-theoutside of the corresponding side frame bar 20 of the frame approximately opposite a corresponding bearing bracket 4| of the inner pair of these bearings, a pair of these shear rubber springs being thereby arranged at each side of the frame in-closely spaced relation to each other and each pair being arranged between the tandem axles 69 and 5 I. Each of these rubber shear springs 65 is preferably constructedas follows:

The numeral 66 represents a rubberbody which is preferably of vertically elongated rectangular cross section lengthwise of the chassis and in opposite vertical section, when the vehicle is unloaded, is of parallelogram form so that its outer face is arranged below its inner face as best shown in Fig. 13. This outer face is vulcanized to a rectangular metal plate 58 the upper part of which is removably secured, as by bolts 99, to a horizontal tie plate or bar l'll in the form of a channel extending lengthwise of the frame with its flanges projecting outwardly. The channel at each side of the vehicle connects the two metal plates 68 of the correspondin pair of rubber shear springs 65.

s The inner face of the rubber body 56 of each rubber shear spring is vulcanized to a rectangular metal back plate H and it will be noted that the metal'back plate 1| extends downwardly beyond the rubber body 66 as illustrated in Fig. 13. The metal back plate ll of each rubber spring .65 is backed by the T-shaped backing plate 12 shown in perspective in Fig. 16.- This backing plate includesan uppercross bar 13 which extends the full width of the back plate H of the rubber spring and a narrower-vertical bar or tongue 14 narrower than the back plate H. When the backing plate 12 is placed against the rear face of the back plate H of the rubber spring, the narrower width of the vertical tongue or bar 14 provides two exposed vertical marginal rails 15 on the rear face of the back plate T l as best shown in Fig. 14.

The lower end of the back plate H is shown as secured to the lower end of the T-shaped backing plate 12 by a pair of bolts 16, as best illustrated in Figs. 13-16. The upper extremities of these plates are shown as connected together by a pair of bolts 18, these bolts also extending through the adjacent frame side bar or channel 20, its liner 2| and the vertical part of the gusset 34 so as to secure the rubber spring to the frame. The rubber spring is further secured to the frame by a second pair of bolts 19 arranged intermediate the upper and lower pairs of bolts 78 and i6 and extending through the back plate H and backing plate 12 of the rubber shear spring and also through the adjacent side frame bar or channel 20, its liner 2| and the vertical part 39 of the supporting bracket 3!.

A pair of rollers 80 ride in the tracks 15 provided on the rear face of the back plate H for each rubber shear spring by the narrow bar or tongue M of the T-shaped backing plate 12. Each of these rollers is journalled on a cross pin 8| and each pair is held in spaced relation by a spacing sleeve 82. The ends of each cross pin extend through apertured ears 83 of a U-shaped bracket 84 and are secured by a pair of nuts 85. The cross part of the U-shaped bracket 84 is disposed against the front face of the front plate 58 of the corresponding rubber shear spring 65 and is shown as secured thereto by a plurality of bolts 86. The yieldin support of the rubber shear springs 65 is provided by vertical movement of the front and back plates 68 and H vulcanized to each rubber body 66, this movement being' illustrated by dotted lines in Fig. 13. With the load transmitted to the upper parts of the front plates 68 by the cross bars 10 the forces are such as to cause the lower ends of the front and back plates 68 and H of each rubber shear spring to separate and hence impose an unnecessary stress on the. vulcanizationbonds between the lower ends of each pair of these plates 63 and H and the rubber body 66 therebetween. The rollers carried by the bracket 84 of each front plate 68 and engaging the rear face of the companion back plate H obviously prevent the separation of thelower ends of these plates and hence prevent such bond stress.

The suspension includes, for each end of each axle, a crank arm journalled on the frame, and shackles connecting each crank arm with an axle bracket on the corresponding axle end. These parts are generally of the form described in greater detail in my copending application for Spring Suspension, Serial No. 153,932, filed April 4, 1950 and to which reference is made for a more detailed description of these parts.

In general, and referring more particularly to the front tandem axle 60, to each end of this axle is secured an axle bracket which supports an axle pivot pin bar 9| at its upper end. The axle bracket 90 is shown as welded at its lower end to the axle end and the axle pivot pin bar 9| is shown as being of square form in cross section and as removably secured by vertical bolts or screws 92 passing therethrough and anchored in the top of the axle bracket 9|.

Each axle pivot pin bar 9| is provided at its opposite ends with generally horizontal, integral axle pivot pins 93 projecting lengthwise of ,the frame 19. The axle pivot pins 93 of each axle pivot pin bar 9| are arranged in generally parallel relation to each other but are out of line and are angularly disposed with reference to the axis of the axle pivot pin bar 9! and. the normal line. of movement of the vehicle. These axle pivot pins converge or toe in toward the front of the vehicle, this providing for self steering of the tandem axles as hereinafter discussed in greater detail.

Each of the axle pivot pins 93 is journalled in the bushing or knuckle 94 of a shackle 95. The bearing between each of these axle pivot pins-93 and its shackle can be lubricated through a lubricant fitting 96.

Each shackle 95 is connected at its opposite end by a universal or ball and socket joint, indicated generally at 98, to a crank arm pivot pin 99 at the outer or free end of a crank arm I00. The construction of the ball and socket joint 98 is described in detail in my said copending application Serial No. 153,932 and is not repeated here. Each crank arm pivot pin 99 extends through a pair of spaced ears HH between which its ball and socket joint 98 is arranged and each crank arm pivot pin 99 is secured to these ears by nuts I02. These ears llll project horizontally outwardly from the body I03 of the crank arm I00, each body I93 extending lengthwise of the frame and having two pairs of such ears, one at each end, and the pairs of cars of each crank arm being connected by a pair of shackles 95 with the axle pivot pins 93 at the opposite endsof a corresponding axle pivot pin bar 9 I.

Asbest shown in Fig. 8, the elongated'body I 03 of each crank arm I00 isprovided at-its op'posite ends with bosses I84'which project hor-' i'zontally in the oppositedirection from the cor-' responding-pairs of ears If. These bosses are provided with bores I85 in each of which a fulcrum-pivot pin I86 is tightly fitted.

At the remote ends of the pair of crank arms I 88 at'each side of the frame, these fulcrum pivot pins I I36 are relatively short and are fitted in a metal sleeve I 88 surrounded by'a rubber bushin I89 and having end rings II8 andIII one'of which is pinned, as at I I2, to the adjacent b'oss-IIWof the crankarm and the other of which is "el'igaged by a nut II3 at the end of the ful- Cltllll' pin I86. Each rubber sleeve I89" is held under-compression in the sleeve 42 of the corre-' spending bearing bracket 4| and permits the necessary degree of oscillation of the corresponding fulcrum pivot pin I86 in itsbearing bracket 4|.

At the adjacent ends of the pair of crank arms I88 at' each side'of the frame, the fulcrum'pivot pins I'I4 are relatively long and project beyond a' metal sleeve II5 fitted thereon. Each metal sleeve I I5 is surrounded by a rubber bushing I I8 and has end rings II 8 and II8 one of which is pinned, as at I28; to the adjacent boss I04 of the crank arm. Each rubber sleeve H6 is held under compression in the sleeve 42 of the corresponding bearing bracket 4| and permits the necessary degree of oscillation of the corresponding fulcrum pivot'pin H4 in its bearing bracket 4I The ends of each-pair of these fulcrumpivot pin's II 4 are arranged in opposed coaxial relationand each pivot pin has keyed thereto a compensating or load transfer arm I2I. Between each pair of compensating arms I2I, the ends of the fulcrum pivot pins I I4 are journalled in bearings I22 in the tubular cylindrical hub I23 of a pinion carrier indicated'generally at I24. Each of these bearings I22 is shown as comprising an inner metal sleeve I25 fitted on a reduced end I26 of the corresponding fulcrum pivot pin H4, an outer metal sleeve I28 fitted in the bore I29 of the corresponding tubular cylindrical hub I23,- and a' rubber bushing I 38 held in compressive relation between the pair of inner and outer sleeves I25 and I28. A tie rod I3-I extends loosely through each pair of the coaxial fulcrum pivot pins II4, this fulcrum rod having a head I32 at its end toward the front of the vehicle and a nut I33 at'its end toward the rear of the vehicle, this last nut engaging the end of the corresponding fulcrum pin II4. A ball thrust bearing I34 is shown asinterposed between the head I32" of each tie rod I31 and the end of the corresponding fulcrum pin I I4.

The pinion-carrier I24 is provided with a centra'lstem I35 projecting laterally from its tubular cyliiidricalhub I23, this stem having a blind bore I36 arranged at right angles to the axis of the hub-I23: ,In this bore I36 is'fitted a-pin I38 which pro'ject'soutwardly therefrom. This'pin I38 is preferably welded in the bore I36 and to this end the"secket"l35 is bored transversely, as indicated atfI35, and'through thesebor'es I39weldm'ents I48" are applied tounitethepin and socketas best shown in'Fi 8.

On theprojecting-end'of each of the pins I36 is 'riiount'ed a pair of antifriction bearings I4I on which is mounted a pinion I42. The teeth of eacli'p'inion mesh with the teeth of a pair of gear segments I43 integral with th 'corresponding pair of compensating'arms' I2I and the gear segments-being concentric'with'the axis of these compensating arms. Dust seals I44'and I45 are provided for thehub of each pinion I42. -It will be seenthat the rotation of one'ofeach pair of.

crank arms I86 through its fulcrum pivot pin I I4, compensating'arm- I2I and its gear segment I43 and through the pinion I42, tendsto rotate the companion'crank arm I88 in the opposite direction through its gear segment I43, compensating arm I2I and fulcrum pivot pin H4.

The extreme outer end of each pin I38 for the corresponding pinion I42 is connected to the corresponding pair of rubber shear springs'65' to provide the yielding connection between the axles and the frame. To this end a pressure head I48 is pinned, asindicated at I41, to the outer or free end of each pin I38 beyond its pinion I42 and this pressure head is provided with an upwardly directed angular pressureface I48 which is shown as being fiat and as inclining upwardly and outwardly relative to the axis of the pin. The transverse axis of this pressure face is horizontally disposed.

This'pressure face engages the lower arcuate pressure face I49 of a-pressure transmittingstrut I58. This lower arcuatepressure face I49 is in the form of a segment of a cylinder, the axis of which is horizontal and parallel with the fulcrum axis of the adjacent pair of crank arms I88. The pressure strut I58 is provided with a similarupper arcuate pressure face I5I also in the form of a segment of a cylinder with itsaxis parallel with the axis of the lower pressure face I49. The upper pressure face I5I is smaller and has a greater degree-of convexity than the lower arcuate pressure face I49. This upper arcuate pressure face I5I bears against the plane pressure face I52 on the underside of aboss I53 projecting outwardly from thechannelor bar 18 con necting the adjacent two rubber springs '65. This pressure face I52'is inclined upwardly and outwardly and its axis lengthwise of the frame is horizontally disposed.

In order to prevent slippage of the pressure strut I50 from between-the plane pressure faces I48 and I52, but otherwise having no function in the transmission of pressure to the rubber shear springs 65; theopposing pressure faces I48 and-I49 are recessed, as indicated at I54-and I55, to receive a-large ball- I56 and the opposing-pressure faces I5I and I52 are similarly recessed, as indicated'at I58 and I58,-to receive a smaller ball I68.

In order to prevent any rebound forces from separating the pressure faces it is'desirable-that the pressure head I48 and boss I53 be tied together. To this end a link I5I is provided. To render this link also effective to protect and conceal the pressure strut I50 aswell as to minimize injury to anyone fingering the parts while the vehicle is being loaded or unloaded, this link is'preferably of U-fo'rm in cross section with its side flange flanking the pressure strut I55. A pivot pin I62 extends through the upper ends of these side flanges and through a bore I63 in the boss I53 parallel with the axes of the arcuate pressure faces I49 and I5I and through a rubber bushing. I64 in this-bore. This bore- I83 is preferably arranged above and slightly to the outside of the ball IE8. A pivot pin I65 extends through the lower ends of these side flanges and througha bore I in the pressure head I48 parallel with the axes of the arcuatepressure faces I43 and I5I- and through a rubber bushing I68 in this bore. This bore I66 is preferably so-"ar ranged that the line ofpressure-of" thepressurc strut I50 swings through the axis of thi pivot pin in the operation of the suspension.

In the operation of the suspension the upward movement of one end of, say, the front axle 90, through the corresponding axle bracket 90, pin bar 9| and axle pivot pin 93, moves the corresponding pair of shackles 95 upwardly so as to swing the outer end of the crank arm I upwardly. This rotates this crank arm I09 about its fulcrum pivot pins I06 and II4 and also swings the corresponding compensating arm I2I keyed to the longer fulcrum pin II4 of the crank arm upwardly. The gear segment I43 at the outer end of this compensating arm I2I so moved upwardly rotates its pinion I42 in a direction to impress a downward pressure on the companion gear segment I43 of the compensating arm I2I of the rear axle BI. This downward pressure of this companion compensating arm I2I is transmitted to the companion end of the rear axle BI through the elongated fulcrum pin II 4, crank arm I00,

shackles 95 and axle bracket 90 fast to this companion end of the rear axle. Accordingly it will be seen that with the present invention there is a load transfer from each end of each tandem axle to the companion end of the other tandem axle whenever there is a differential in upward movement of the axles so that the load is always shared by the companion ends of the two tandem axles.

Under the assumed operation, that is with one end of the front tandem axle moving upwardly with the other wheels on the ground, the compensating arm I2I and gear segment I43 of the companion end of the rear tandem axle BI is,

of course, held stationary and hence the upward movement of the compensating arm IZI and gear segment I43 associated with the end of the front tandem axle moving upwardly causes its pinion bar or channel I0 at the corresponding side of the vehicle.

The opposite ends of this fore-and-aft connecting bar or channel ?0 are connected to the front plates 68 of the companion pair of the rubber springs 65 and hence this movement is transmitted to the rubber bodies 06 of these springs. Since the back plates II of these rubber springs are fixed through the T-shaped backing plate I2 to the vehicle frame I3, this upward movement of the outer plates 68 of these rubber springs places these rubber bodies under vertical shear stress, these rubber bodies providing the resilient resistance to the assumed upward movement of one end of the front tandem axle 60.

Since the upward pressure is impressed on the front plates 58 of the pair of rubber springs 35 under consideration by the fore-and-aft bar or channel I0 connecting these plates, this upward pressure, in the absence of provision to prevent it, would tend to separate the lower ends of these front plates 68 from the back plates II of the rubber springs and hence tend to destroy the vulcanization bond between the lower ends of these rubber bodies 59 and their front and back plates 38 and II. To preventsuch bond stress the pair of rollers 80 connected through the brackets 84 with the front plates 98 of these rubber springs 55 ride on the rails 15 provided on the back plates II of these rubber springs 05 by the T-shaped backing plate I2. These rollers prevent separation of the lower end of each front plate 08 from the lower end of the corresponding back plate II and hence prevent such bond tress.

In the unloaded condition of the truck the rubber bodies 60 of the rectilinear shear springs 65 are in the full line position shown in Fig. 13 in which the front plates 08 thereof are arranged below the companion back plates II and the cross section of the rubber body, transversely of the vehicle, is in the form of a downwardly and outwardly inclining parallelogram. In the normal loaded condition of the truck the front plate 68 of the rectilinear shear springs 65 have been moved upwardly'to the first dotted line position shown in Fig. 13 in which position the rubber bodies 56 have been distorted so as to be of rectangular form in cross section, transversely of the vehicle. Under extreme load conditions, as when both axles are moved upwardly on encountering bump in the road, and when fully loaded, the front plates 68 of the rectilinear shear springs move upwardly to the extreme dotted line position shown in Fig. 13 in which the rubber bodies 56 have been stressed to have a cross section, transverse of the vehicle, in the form of an outwardly and upwardly inclining parallelogram. When the load or pressure imposed upon the rubber bodies 56 of the pair of rectilinear shear outwardly and upwardly inclining parallelogram. When the load or pressure imposed upon the rubber bodies 60 of the pair of rectilinear shear springs 65 at eachside of the vehicle is relieved, these rubber bodies. tend to assume the full lin position shown in Fig. 13.

A feature of the invention resides in the action of the pressure struts I50 as illustrated in Figs. 9-12. In the normal unloaded condition of the truck, as illustrated in Fig. 11, the line of contact between the faces I49 and I 48 of the pressure strut I50 and pressure head I46, respectively, is remote from the frame I9. Smilarly the line of contact between the faces I5! and I52 of the pressure strut I50 and boss I53, respectively, is close to the frame I9.

Starting with the unloaded or free spring condition shown in Fig. 12, as the truck is loaded the stem I and its pin I38 and pressure head I moveupwardly about the axis of the fulcrum pins II4 and I03 and the arcuate face I49 of the pressure strut I rolls upon the fiat face I48 of the pressure head I46 so that the line of contact between these faces moves outwardly away from the frame III as llustrated by comparing the unloaded position, Fig. 12, with the normally loaded position, Fig. 10, this normally loaded position being also illustrated in Fig. 9. The arcuate face I5I of the pressure strut I50 rolls upon the flat face I52 of the boss I53 so that the line of contact between these faces moves away from the frame I9.

When maximum load is encountered, as illustrated in Fig. 11, the arcuate face I49 of the pressure strut I50 rolls to the outer extremity of the flat face I48 on the pressure head I40 so that the line of contact between these faces moves still further from the frame I9. The line of pressure between the arcuate face I5I of the pressurestrut I50 and the fiat face I52 of the boss I53 moves still further from the frame I9.

It will be noted that a pure .rollingaction is the transmission of pressure but'merely serves ,to prevent'separation of the pressure head M6 from the boss I53 as might occur under rebound action. The rubber bushings I64 and H58 for this i link 16! permit such slight differential movement of the pivots IE2 and IE5 relative to the lines of contact of the pressure faces l5] andl49 of the compression strut I50 as may occur. The U- shaped form of this link 8| also in part encloses the pressure strut I 56 both to protect it and also -to protect against possible injury to anyone fingering the suspension while it is working.

It will be noted that the shackles 95 are inclined upwardly and inwardly from their respectivecrank arm pivot pins fle to the corresponding axle pivot pins 93. This upwardand inward .inclinedarrangement of the :shackles tends to cause each axle to centralize itself in a direction -tra-nsverse of the frame and enables the action 7 of ,gravity to geometrically and resiliently resist .any movement of either axle away from its central position. .This'permits the vehicle frame [9 to move substantiallystraight ahead despite a .certain amount of lateral movement of the axles. This .arrangement'of the shackles further prov videshigh and-wide pivot positions which provide .increased stabilityin that these high and wide pivot positions provide effective spring centers lwhichcan be as wideor wider than the track of the vehicle. Further, this arrangement reduces side sway, the high and wide pivot positions, together with the upward and inward slant .of the shackles, providing a suspension in which the frame is more nearly suspended than mount- .ed. Other important advantages which flow fromthe inclined arrangement of the shackles as shown .are the reduction in the possibilityof wheel tramp and in the elimination of the need for. antibody-roll devices,-such as torsionbarstabilizers.

The oblique positionof the axes of the axle .pivot pins 93 of the pin bar 9| on each axle causes .either wheel 62 to move freely a short distance rearwardly whenever said wheelrises .and, concomitantlycauses this wheel to move. a short distance forwardly whenever said wheel falls. This enables the peripheral speed of the wheel to. be maintained substantially constant when traveling overirregularities in the road, .and, at the same time, enables the axle otthe Wheel to receive the sudden horizontal thrusts h which inevitably result asa consequence of the .uniformiperipheral speed of the wheel, without imparting these thrusts directly to the frame. I 'When the vehicle is traveling straight ahead, if the tandem axles 60, 6! are not parallel for any reason, they will automatically assumea parallel'position because of the fact that if, for ex- 1 ample, the rear axle'Bl is out of line it will tend to follow a horizontal arc and this tendency, due to' the lateralfriction between the tires .and' the "roadway, will cause a lateral "movementbf the 1 axle relative to the frame. Due to the fact that the shackles ,95 normally extend upwardly and .inwarclly, this lateral movement is automatically caused to be translated into a slight .turning 12 movement, in a horizontal-plane, -,of the whole axle, and this turning movement will continue 'until'both the tandem axles are in line witheach other. Such a movement-naturally, causes'a change in the angularity of the shackles 95;.at the opposite end of each axle and this change is resisted by gravity which, due to the obliquity of the shackles, is caused to act in a, geometric manner. Thisobliquity of the axle pivot pins 93 is preferably such that when oneof the tandem .axles moves axially its :maximumextent, the wheel 62 at one end thereof Willmove forwardly about 3 of an inch and the wheel 62 at the opposite endthereof will move rearwardly about 3A1 ofan inch.

Due to the obliquity or toeing in of the axle pivot pins 93 the tandem axles-5! 6| are renroad. Thus, these axles tend to trail or-follow 'eachother when making a turn in the road-as well as when going straight ahead. In making a-turn, just as whenjgcing straight ahead the tires naturally tend to resist lateral scuffingand tend to push the axles laterally and, as aconsequence, each axle moves obliquely to eliminate scuffing. Thus, when the vehicle is making'a turn the two rear axles are caused to move automatically to such an oblique :position,"relatively to each other, as will :cause their axes to intersect the axis of revolution of the "two front wheels, and enables the-vehicle to'rmakethe turn without tirescufrlng. -'I-his;action occurs when either the vehicle'is steered-around a long turn in the road or "when it is steering sharply on a smooth :road, as, for instance, when passing a slow vehicle ;or.otherwise avoiding some obstruction. .Eitheriaxle also tends to assume-a slight oblique position when a ten'dencyto tire scuffing occurs because 'of one wheel-or a pair ofwhe'els at one end of either axis has a diameter different from the wheel or pair of wheels :at the other end of the same axle. Accordingly, tire scuffing when tires of different diameters are used is reduced by the practice of the present invention.

"To provide such automatic steering and at the same time reduce the space required for the suspension between the body andthe tires for accommodation of the suspension,.the axle-pivot pins-93 of each pivot pin bar 9|, while parallel, are arranged outof line with each other so'as to reduce the space requirement between the frame and each tire of the tandem axle suspension to accommodate these pivot pins and the shackles and crank arm which they connect. With the'p'ivot pins 930i each pivot pin bar out of line, the shackles Ed'necessarily twist slightly relative to the crank arms- I00 as they move vertically with'their axle and'hence the balland socket joints 98 are required between each shackle 95 and its crank arm I00. However, this arrangement of the angular pivot pins 93 and the inclusion of the ball and socket joints 98 permits the suspension to be used with trucks having a wide frame and large tires.

It willparticularly be noted that asthe line contact between the facesMB and MB of the pressure head Hit and pressure strut l5llmoves inwardly on increase of load (Figs. 11, 10, and 12) the effective length of the lever arm comprising the pinion-carrier (24 and pressure head I46 decreases. Conversely, of course, on decreasing load the effective length of this lever arm increases.

This provides a variable rate spring suspension that there is decreasing leverage as the load is increased and hence the rubber springs 65 are 13 compressed more readily as the load increases. The variable rate spring action so provided by the changing effective length of this lever arm is not effected by the moving line of contact between the surfaces l and I 52 of the pressure strut I50 and boss [53, respectively.

From the foregoing it will be seen that the present invention provides a tandem axle suspension in which the resilience is provided by rubber bodies subjected to a rectilinear shear action and at the same time provides a suspension in which there is a load transfer from one axle end to the companion axle end so as to equalize the load on both axles; in which the axles tend to aline themselves and also are self-steering so as to move to such angularity as avoids tire scuffing when making a turn in the road; and in which the unsprung weight is reduced to a very low value. It will further be seen that this suspension is simple and compact, considering the function which it performs; is adapted to vehicles having wide bodies and large tires; and accomplishes the various other objectives set forth.

By rubber as used in the accompanying claims is meant both natural rubber and also synthetic rubber and mixtures of natural and synthetic rubber.

I claim:

1. In a tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof and said suspension having a load transfer mechanism at each side of said frame pivotally connecting the corresponding ends of said axles and arranged to equalize the loads on said ends, the combination therewith of a resilient support for said frame, comprising a pair of rubber blocks spaced lengthwise of said frame and arranged adjacent each of said load transfer mechanisms, means securing one face of each rubber block to said frame in position to permit flexure of said block and vertical movement of the opposite face thereof, a metal plate bonded to said opposite face of each rubber block, a horizontal bar connecting the plates of each pair of rubber blocks, and means operatively connecting each of said bars with the corresponding load transfer mechanism.

2. In a tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof and said suspension having a load transfer mechanism at each side of said frame pivotally connecting the corresponding ends of said axles and arranged to equalize the loads on said ends, the combination therewith of a resilient support for said frame, comprising a pair of rubber blocks spaced lengthwise of said frame and arranged adjacent each of said load transfer mechanisms, means securing one face of each rubber block to said frame in position to permit flexure of said block and vertical movement of the opposite face thereof, a metal plate bonded to said opposite face of each rubber block, a horizontal bar connecting the plates of each pair of rubber blocks and a vertical pressure strut operatively connecting each of said bars with the corresponding load transfer mechanism. 7

3. In a tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on theends thereof and said suspension having a load transfer mechanism at each side of said frame pivotally connecting the corresponding ends of said axles and arranged to equalize the loads on said ends, the combination therewith of a resilient support for said frame, comprising a rubber block arranged above each of said load transfer mechanisms and inter mediate said frame and wheels, means securing one face of each rubber block to said frame in position to permit fiexure of said block and vertical movement of the opposite face thereof, a metal plate bonded to said opposite face of each rubber block, and a vertical pressure strut operatively connecting each of said plates with the corresponding load transfer mechanism.

4. In a tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof and said suspension having a load transfer mechanism at each side of said frame pivotall connecting the corresponding ends of said axles and arranged to equalize the loads on said ends, the combination therewith of a resilient support for said frame, comprising a rubber block arranged above each of said load transfer mechanisms and intermediate said frame and wheels, means securing one face of each rubber block to said frame in position to permit flexure of said block and vertical movement of the opposite face thereof, a metal plate bonded to said opposite face of each rubber block, a vertical pressure strut operatively connecting each of said plates with the corresponding load transfer mechanism, and a vertical link alongside each strut and pivotally connecting the adjacent plate and load transfer mechanism to prevent separation of said pressure struts from said plates and load transfer mechanisms under rebound reactions of the suspension.

5. In a tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof and said suspension having a load transfer mechanism at each side of said frame pivotally connecting the corresponding ends of said axles and arranged to equalize the loads on said ends, the combination therewith of a resilient support for said frame, comprising a rubber block arranged above each of said load transfer mechanisms and intermediate said frame and wheels, means securing one face of each rubber block to said frame in position to permit fiexure of said block and vertical movement of the opposite face thereof, a metal plate bonded to said opposite face of each rubber block, a vertical pressure strut operatively connecting each of said plates with the corresponding load transfer mechanism, and a vertical link alongside each strut and pivotally connecting the adjacent plate and load transfer mechanism to prevent separation of said pressure struts from said plates and load transfer mechanisms under rebound reactions of the suspension, said links each having flanges at leas in part enclosing the companion strut.

6. In a tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof and said suspension having a load transfer mechanism at each side of said frame pivotally connecting the corresponding ends of said axles and arranged to equalize the loads on said ends, the combination therewith of a resilient support for said frame, comprising a rubber block arranged above each of said load transfer mechanisms and inter 15 mediate-said frame and Wheels, means securing ;onetface of eachrubber blockto said frame in position to:' permit, flexure of said block and vertical :movement ofthe opposite face thereof, a metal plate bondedto said opposite face of each rubberrblock, a vertical pressure strut opera- ,tively1connecting each' of said plates with the corresponding load transfer mechanism, .a vertical link .arrangedalongside each strut, a pivot pin embraced by a rubber bushing connecting "the-upper end of each link with the correspond ing plate,iand"a pivot .pin embraced by a rubber bushingconnectingthe lower end of each link :withthe corresponding load transfer mechanism,

said links .preventing'separation of said pressure s'truts fromzsaid plates and load transfer mechanisms under rebound reactions of the suspen .7. ma tandem axle vehicle spring suspension adapted tobe interposed between a vehicle frame :a'ndga pair of tandem axles each having wheels iourn'alled on the ends thereof and said suspension having a load transfer mechanism at eachside of said frame pivotally connecting the corresponding ends of said axles and arranged ,to equalize the loads on said ends, the combination therewith of a resilient support for said frame, comprising a rubber block arranged above each of said load transfer mechanisms and intermcdiatesaid :frame and wheels, a back plate bondedto the vertical side of each of said rubber blocks facing said frame, means securing each back plate to said frame in position to per- -mit'vertical'flexure; of its rubber block and vertical movement of theside of its rubber block "opposite said back plate, a'front plate bonded to saidopposite'side of each'rubber block, a vertical pressure strut operatively connectingthe uppertpart'of each'ofsaid'front plates with the corresponding load transfer mechanism, and

-means preventing-separation of the lower ends of" said plates of each rubber block, comprising a roller onone of said plates and a vertical track on the other of said plates and on which said roller rides.

8.In a tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and atpair of'tandemaxles each having wheels journalled on the ends'thereof and said suspension having a load transfer mechanism at each side: of said-frame pivotally connecting the corresponding ends of said axles and arranged to equalize the loads onsaid ends, the combination therewith of a resilient support for said. frame,

comprising a rubber block arranged above each i of said load transfer mechanisms intermediate said frame and wheels, a vertical back plate bonded to the vertical side of each of said rubber blocks facing said frame, a T-shaped backing plate secured to the face of each back plate opposing said frame and having a vertical tongue providing marginal tracks along the vertical .edges of each back plate and facing said frame, means arranged to secure each T-shaped backing plate to said frame in position to permit vertical .flexure of the rubber block associated therewith and vertical movement of the side of said rubber block :opposite said back plate, a front plate bonded tosaid opposite side of each rubber block, a vertical pressure strut operatively connecting the upper part of each of said front plates with the corresponding load transfer mechanism, and means preventing separation of the lower ends of ,the plates of each rubber block, comprising ears at the sides of each of said front plates and ar- :16 ranged' alongside the corresponding back; plate, a pinconnecting each pairofsaid ears and arranged on the side 'of the'back plate remote from and a pair of tandem axles each having wheels journalled on the ends thereof, comprising a normally generally horizontal crank arm arranged above each end of each axle and journal-led on said frame to swing abouta fulcrum axis extending lengthwise of said frame, a'shackle connecting the free end of each crank arm with the adjacent axle'end, a: pair of gears with opposing teeth at each side-ofthe vehicle and each fast to one-of the opposing ends of 'a corresponding crank arm concentric with said fulcrum axis thereof, a-pinion carrier journalled to swing about an axis concentric with each fulcrumaxis and arrangedat the opposing ends of the corresponding pair of said crank arms, a pinion journalled on the free end of each of said pinion-carriers and meshingwith the opposing teeth of the adjacent pair of said gears, and means on said frame and yieldingly resisting upward movement of said free end of each of said pinion'carriers, comprising a pressure head mounted on the free end of each pinion carrier and having an upwardly directed pressure face, a pressure strut having a downwardly directed pressure face engaging said pressure face of each pressure head and having an upwardly directed pressure face at its upper end, a spring abutment member above each pinion carrier and having a downwardly directed pressure face engaging said upwardly directed pressure face of the corresponding pressure strut, and yielding meansconnecting each of said spring abutment members and said frame and guiding each spring abutment member to me ve vertically relative tosaid frame.

10. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof, comprising a normally generally horizontal crank arm arranged above each end of each axle and journalled'on said frame to swing about a fulcrum axis extending lengthwise of said frame, a shackle connecting the free end of each crank arm with the adjacent axle endya pair of gears with opposing teeth at each side of the vehicle and each fast to one of the opposing ends of a corresponding crank arm concentric with said fulcrum axis thereof, a pinion carrier iournalled to swing about an axis concentric with each fulcrum axis and arranged at the opposing ends of the corresponding pair of said crank, arms, a pinion journalled on the free end of each of said pinion carriers and meshing with the opposing teeth of the adjacent pair of said gears, and means on said frame and yieldingly resisting upward movement of said free end of each of said pinion carriers, comprising a pressure head fixed to the free end of each pinion carrier and having an upwardly directed pressure face, a pressure strut having a convex arcuate downwardly directed pressure face curving about an axis generally parallel with the adjacent fulcrum pins and having rollingengagement with the pressure face of the corresponding pressure head, each pressure strut also having a convex arcuate :upwardly directed pressure face curving about an axis generally parallel with the adjacent fulcrum pins, an; abutment member above each 17 i pinion carrier and having a downwardly directed pressure face having rolling engagement with said upwardly directed pressure face of the corresponding pressure strut, and yielding means connecting each of said spring abutment members and said frame and guiding each spring abutment member to move vertically relative to said frame.

11. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof, comprising a normally generally horizontal crank arm arranged above each end of each axle and journalled on said frame to swing about a fulcrum axis extending lengthwise of said frame, a shackle connecting the free end of each crank arm with the adjacent axle end, a pair of gears with opposing teeeth at each side of the vehicle and each fast to one of the opposing ends of a corresponding crank arm concentric with said fulcrum axis thereof, a pinion carrier journalled to swing about an axis concentric with each fulcrum axis and arranged at the opposing ends of the corresponding pair of said crank arms, a pinion journalled on the free end of each of said pinion carriers and meshing with the opposing teeth of the adjacent pair of said gears, and means on said frame and yieldingly resisting upward movement of said free end of each of said pinion carriers, comprising a pressure head fixed to the free end of each pinion carrier and having an upwardly directed pressure face, a pressure strut having a convex arcuate downwardly directed pressure face curving about an axis generally parallel with the adjacent fulcrum pins and having rolling engagement with the pressure face of the corre sponding pressure head, each pressure strut also having a convex arcuate upwardly directed pressure face curving about an axis generally parallel with the adjacent fulcrum pins, an abutment member above each pinion carrier and having a downwardly directed pressure face having rolling engagement with said upwardly directed pressure face of the corresponding pressure strut each of said pressure faces being provided with a recess and said recesses of each pair of contacting faces being in register with each other, an alinement member in each registering pair of said recesses and bridging the corresponding pair of said contacting faces, and yielding means connecting each of said spring abutment members and said frame and guiding each spring abutment member to move vertically relative to said frame.

12. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof, comprising a normally generally horizontal crank arm arranged above each end of each axle and journalled on said frame to swing about a fulcrum axis extending lengthwise of said frame, a shackle connecting the free end of each crank arm with the adjacent axle end, a pair of gears with opposing teeth at each side of the vehicle and each fast to one of the opposing ends of a corresponding crank arm concentric with said fulcrum axis thereof, a pinion carrier journalled to swing about an axis concentric with each fulcrum axis and arranged at the opposing ends of the corresponding pair of said crank arms, a pinion journalled on the free end of each of said pinion carriers and meshing with the opposing teeth of the adjacent pair of said gears, and means on said frame and yieldingly resisting upward movement of said free end ofeach of said pinion carriers, compris ing a pressure head mounted on the free end of each pinion carrier and having an upwardly directed pressure face, a pressure strut having a downwardly directed pressure face engaging said pressure face of each pressure head and having an upwardly directed pressure face at its upper end, a spring abutment member above each pinion carrier and having a downwardly directed pressure face engaging said upwardly directed pressureface of the corresponding pressure strut, yielding means connecting each of said spring abutmentmembers and said frame and guiding each spring abutment member to move vertically relative to said frame, and means preventing separation of each pressure head and its spring abutment member fromthe pressure strut therebetween under rebound reactions'of said suspension, comprising a vertical link associated with each strut, a pivot pin connecting the upper part of each link with the corresponding spring abutment member, and a second pivot pin connecting the lower part of each link with the corresponding pressure head.

13. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame and a pair of tandem axles each having wheels journalled on the ends thereof, comprising a normally generally horizontal crank arm arranged above each end of each axle and journalled on said frame to swing about a fulcrum axis extending lengthwise of said frame, a shackle connecting the free end of each crank arm with the adjacent axle end, a pair of gears with opposing teeth at each side of the vehicle and each fast to one of the opposing ends of a corresponding crank arm concentric with said fulcrum axis thereof, a pinion carrier journalled to swing about an axis concentric with each fulcrum axis and arranged at the opposing ends of the corresponding pair of said crank arms, a pinion journalled on the free end of each of said pinion carriers and meshing With the opposing teeth of the adjacent pair of said gears, and means on said frame and yieldingly resisting upward movement of said free end of each of said pinion carriers, comprising a pressure head mounted on the free end of each pinion carrier and having an upwardly directed pressure face, a pressure strut having a downwardly directed pressure face engaging said pressure face of each pressure head and having an upwardly directed pressure face at its upper end, a spring abutment member above each pinion carrier and having a downwardly directed pressure face engaging said upwardly directed pressure face of the corresponding pressure strut, yielding means connecting each of said spring abutment members and said frame and guiding each spring abutment member to move vertically relative to said frame, and means preventing separation of each pressure head and its spring abutment member from the pressure strut therebetween under rebound reactions of said suspension, comprising a vertical link having vertical side flanges embracing the corresponding pressure strut, a pivot pin connecting the upper part of each link with the corresponding spring abutment member, a second pivot pin connecting the lower part of each link with the corresponding pressure head, and a rubber bushing embracing at least one of said pins and providing a yielding connection between said one of said pins and one of the two parts connected thereby.

14. A tandem axle vehicle spring suspension 19 wa te my be infiemas em n a ehi i r r z e m a flai facele n a ac Wi wh l waali qifi ai S fihei qf! e mrir ii a n9?- iizal y gene a hofiz ntal c an a m a ra aha? em; M eaqha l a d i urn le o a m ne to Wi a a u fl axis 'exfi d- 'fi rin hv aid K m? a a e Q mg he e .6 qi' h @iafi m with th a i eil axi nd a ai 9 ea s wan i posin teeth a an?! e. 9f h h cl d ea h f t0 one oi the pp'csin g ends cf a correspondin cr k rm, iqemyic w t sa il mm ax e 9 8 piai neqa c er 'Qn aafle to Swing b ut n j ritric ith i fu c'mm. i n a Y a the noeing @I QS" 9 h c es n n air .Q aid mm; a ms. iniQ imlr al ed on he fr e ea 9 a h n a d p m n e fia a ms ng wi h he ep s' n teeth o the ad c pair o' f said gears; a rubber block in vertically spaced relatioh to eaeh'pirgiqn carrier, means 5& ur (mp vertical face of each rubber block to said frame in position tc permit fiexure of said block and vertical movement, of the opposite vertical face thereof, and means operatively connecting said opposite vertical face of each rubber block t9 the corresponding pinion carrier ALBERT F. HZECKMAN.

References Cited in the fil e of: this p tent UNITED STATES PATENTS- 

